The present invention relates to a graphic display control method and apparatus which use an interlace type cathode ray tube (CRT).
In a conventional raster scan type graphic display, when a diagonal line is to be displayed, it is displayed stepwise because light points are only provided at picture cells on raster lines. Accordingly, a smoothly continuous diagonal line could not be displayed.
In order to resolve the above problem, it has been proposed to construct each point by a plurality of picture cells capable of being imparted with different luminances, and change the luminances in accordance with fractions derived by calculating coordinates of points on the diagonal line so that the diagonal line is displayed as a smooth line by the change of the luminances of the picture cells. FIGS. 18 and 19 show examples of the diagonal lines displayed by the luminance modulation type graphic display. In FIGS. 18 and 19, black block areas represent the luminances of the respective picture cells.
However, in this luminance modulation type graphic display, the line width is large and not uniform because each of the points forming the line consists of a plurality of picture cells.